Spinlock Deckvest 5D 170N Pro Sensor Inflatable PFD & Harness Very light, comfortable design for use over long periods This is a water sensitive activation system that uses a compressed paper capsule which dissolves when wet which then releases a spring to puncture the CO2 cylinder. The cap is designed so that only water flowing upwards through the unit will cause it to activate. Water, spray and rain running down the jacket will not cause activation. The Pro Sensor has two indicators that show the status of the CO2 cylinder and firing head. The UML Pro Sensor is a very reliable system which is easy to check and re-arm. It is also easy to convert to manual firing only. Re-arming kits for this inflation system are stocked by most marine stores.